Techniques for drawing optical waveguide fibers are well known in the art. See, for example, DiMarcello et al., "Fiber Drawing and Strength Properties," Optical Fiber Communications, ed. T. Li, Vol. 1, Academic Press Inc., pages 179-248 (1985) and the references cited therein.
A schematic of an optical fiber drawing line is shown in FIG. 1. Furnace 50 heats preform 10 to a temperature great enough to allow bare fiber 13 to be drawn therefrom by tractor mechanism 32.
Bare fiber diameter monitor 52 in combination with a suitable process control system ensures that the bare fiber is drawn to a specified outside diameter, e.g., 125 microns. In order to provide rapid, high accuracy measurements of the fiber diameter, monitor 52 generally employs an optical technique of the interference type as disclosed in Watkins, U.S. Pat. Nos. 3,982,816 and 4,067,651. See also Murphy et al., U.S. Pat. No. 4,280,827. Since such monitors use an interference pattern to make the diameter measurement, they are often referred to as "IDMs".
Hermetic coating reactor 54 is used to coat the fiber with a thin hermetic coating, e.g., a carbon coating having a thickness of around 500 angstroms. See, for example, DiMarcello et al., U.S. Pat. No. 5,000,541, Ishiguro et al., U.S. Pat. No. 5,035,484, and Schultz et al., U.S. Pat. No. 4,735,856. Such coatings have been found to reduce absorption of water and hydrogen into the fiber.
Hermetic coating monitor 64 in combination with the process control system ensures that the hermetic coating has a substantially constant thickness. Kingsbury, U.S. Pat. No. 5,142,228, shows a suitable construction for such a monitor. Other monitors are disclosed in Frazee, Jr. et al., U.S. Pat. No. 4,952,226, Atkins et al., U.S. Pat. No. 5,013,130, Inoue et al., "Development of Non-Contact Coating Thickness Monitor for Hermetically Carbon Coated Fiber," Conference Digest for the proceedings of the Optical Fibre Measurement Conference, September 1991, York, England, pages 135-138, and commonly assigned, copending application Ser. No. 08/011,393, filed Jan. 29, 1993 now U.S. Pat. No. 5,408,308 and entitled "Method for Monitoring Hermetically-Coated Fibers."
Protective coating applicator 56 in combination with curing apparatus 58 applies a protective coating, e.g., a UV-curable acrylate coating, to the hermetically-coated fiber. Coated fiber diameter monitor 60 is used to control this process. Application of the protective coating completes the drawing process and the finished fiber 22 is collected on a take-up spool or reel for storage and distribution.